The present invention relates to a rotor for alternators and, more particularly, to an alternator rotor suited for use in alternators mounted on vehicles.
A typical alternator rotor designed for use on vehicles has, as disclosed in the specification of the U.S. Pat. No. 3,253,167, a rotary magnetic pole assembly composed of a pair of claw-type magnetic pole segments, field coils disposed in the magnetic pole assembly, a rotor shaft extending through the center of the rotary magnetic pole assembly and supported by bearings, a pair of slip rings arranged on one end of the rotor shaft with an insulator interposed between the slip rings, and cooling fans attached to both axial end surfaces of the rotary magnetic pole assembly. Thus, the known alternator rotors have common features that the cooling fans are attached to both end surfaces of the rotary magnetic pole assembly and the slip rings for supplying the field coils with electric current are fixed to one end of the rotor shaft. This arrangement affords a high cooling efficiency and a high output power by virture of the cooling fans incorporated in the rotor. However, since the slip rings are usually fabricated separately from the rotor shaft and then forced onto the rotor shaft, the force by which the slip rings are fixed is inevitably small and the diameter is liable to be increased disadvantageously.
In some cases, the rotor shaft and the slip rings are united by molding with an insulating material. This, however, suffers from the following disadvantages due to the fact that the parts have to be properly placed in the mold.
(1) The size of the mold is increased. PA1 (2) A long time is required for pre-heating the rotor shaft. PA1 (3) The portions of the rotor shaft which are to be born by bearings have to be mechanically finished after the molding.
It is to be pointed out also that, since the portion for supporting the slip rings is constituted by a reduced-diameter portion of the rotor shaft, such portion tends to be deformed by cutting resistance during the final machining of the outer face of the rotary magnetic pole assembly.